The subject of the present invention is a geared motor unit, particularly for driving vehicle equipment such as window lifters, sunroofs, etc, and of the type comprising a rotor equipped with a rotor shaft, a reduction gearbox which contains a gearwheel in mesh with a worm belonging to the shaft and capable of driving an output member.
Geared motor units of this type are normally equipped with means for adjusting the axial play between one end of the rotor shaft and the wall of the box. This is because the axial play in the driveline mounted in the geared motor unit is due to the combination of dimensional spreads on the various parts on assembly (shaft, endstop, box, etc.) which, placed end to end, are not as long as their housing.
Hitherto this axial play has been compensated for manually using a screw housed in the end of the box facing the rotor shaft hole and which is immobilized by an adhesive which at the same time provides sealing. Such a method of adjustment is lengthy to perform, expensive, and increases the overall cost of manufacture of the geared motor unit.
It is also known practice (see U.S. Pat. No. 5,169,245) to achieve automatic compensation for the axial play in the driveline of the geared motor unit using a coil spring resting in an axial housing of the end of the box, and a system of end stops designed to limit the compressive axial loading experienced by the coil spring to a predetermined value. This limitation is achieved by a shoulder on the inside of the wall of the box, and against which a piston inserted between the end of the shaft and the coil spring abuts.
Patent Abstracts of Japan Vol. 018 No. 297 of 7.6.1994 also discloses a geared motor unit in which an end stop, fixed by welding to one end of the box, eliminates any axial play between the rotor shaft and the wall of the box.
These devices for compensating for the axial play have a drawback which lies in the fact that they are not able to eliminate the troublesome noise of the shaft which is caused when it changes its direction of rotation.
The object of the invention is therefore to eliminate this drawback by arranging the geared motor unit in such a way that these noises are completely eliminated.
According to the invention, the geared motor unit comprises means for eliminating, under a given compressive axial preload, any axial play between one end of the rotor shaft and the wall of the box.
According to one embodiment of the invention, the said means comprise a plug housed in the end of the box, and a piston inserted between the plug and the end of the shaft, the plug exerting the said compressive axial preload, set at the time of assembly, on the piston and on the shaft, and the box by melting the plastic of which the box is made into the said roughnesses; this melting may be obtained, for example, using a sonotrode, an ultrasonic-welding machine, or alternatively by high-frequency welding.
According to another possible embodiment of the invention, the geared motor unit comprises a metal plug mounted so that it can slide in an axial housing formed in the wall of the box facing the end of the shaft; irregularities are arranged on the surface of this plug in contact with the wall of the housing, and the plug is moved axially until it comes into abutment against the end of the shaft under a given compressive axial preload thrust, then immobilized in this position so as to eliminate any shaft play.
This type of embodiment therefore has no piston, the plug alone fulfilling the function of plug and piston of the previous embodiment, and being immobilized in the desired position to exert appropriate axial thrust on the shaft.
The basic idea underlying the invention therefore consists in eliminating the axial play left in geared motor units of the state of the prior art and in doing so under a given compressive axial preload or thrust, for example of the order of 100 newtons.